Exhaust heat recovery apparatus

ABSTRACT

An evaporator has tubes, and evaporates working fluid therein by heat of exhaust gas. A condenser emits heat of the working fluid toward coolant so as to condense the working fluid, and returns the condensed working fluid to the evaporator. A fin for increasing an area for transmitting heat is disposed between the tubes, and is connected to the tubes. The fin has an operation force reducing part for reducing an operation force applied to the fin in accordance with a thermal expansion difference between the tubes. The operation force reducing part is disposed at a midpoint of the fin between the tubes.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2006-106786 filed on Apr. 7, 2006, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust heat recovery apparatus. For example, the recovery apparatus is typically used in a vehicle having an internal combustion engine, and recovers exhaust heat from the engine.

2. Description of Related Art

JP-A-7-120178 discloses an exhaust heat recovery apparatus including a heat siphon, in which an evaporator and a condenser are connected in a loop. The evaporator includes plural tubes, and is disposed in an exhaust pipe of an engine. The condenser is disposed at a coolant side of the engine, and recovers exhaust heat from the engine into coolant.

In order to promote heat-exchange between thermal media and exhaust gas in the evaporator, a fin is brazed to an outer surface of the tube so as to increase a thermal transmission area.

However, when a temperature distribution is generated in a flow of exhaust gas having high temperature, a temperature difference may be generated between the tubes in accordance with the temperature distribution. Therefore, a thermal expansion difference may be generated between the tubes, and a tensile load may be applied to the fin. For example, a rupture may be generated in a fillet between the tube and the fin.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of the present invention to provide an exhaust heat recovery apparatus.

According to an example of the present invention, an exhaust heat recovery apparatus includes an evaporator and a condenser. The evaporator has a plurality of tubes arranged in an arrangement direction, and a fin for increasing an area for transmitting heat. The evaporator evaporates working fluid therein by heat of exhaust gas discharged from an internal combustion engine. The condenser emits heat of the working fluid flowing from the evaporator toward coolant of the internal combustion engine so as to condense the working fluid, and returns the condensed working fluid to the evaporator. The fin is disposed between the tubes in the arrangement direction, and is connected to a face of the tube. The fin has an operation force reducing part for reducing an operation force applied to the fin in accordance with a thermal expansion difference between the tubes in a tube longitudinal direction. The operation force reducing part is disposed at a midpoint of the fin in the arrangement direction.

Accordingly, the fin can be restricted from being damaged by the thermal expansion difference between the tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing an exhaust heat recover apparatus, according to a first embodiment of the present invention, mounted in a vehicle;

FIG. 2 is a schematic cross-sectional view showing the exhaust heat recover apparatus;

FIG. 3 is an enlarged cross-sectional view of tubes and fin layers of the exhaust heat recover apparatus;

FIG. 4 is an enlarged cross-sectional view of tubes and fin layers of the exhaust heat recover apparatus;

FIG. 5 is an enlarged cross-sectional view of tubes and a fin of an exhaust heat recover apparatus according to a second embodiment;

FIG. 6 is an enlarged cross-sectional view of tubes and a fin of the exhaust heat recover apparatus according to the second embodiment; and

FIG. 7 is a schematic cross-sectional view showing an exhaust heat recovery apparatus according to a third embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

An exhaust heat recovery apparatus 100 in a first embodiment will be described with reference to FIGS. 1-3. The apparatus 100 is used in a vehicle having an engine 10 as a driving source, and disposed between an exhaust pipe 11 and an exhaust heat recovery circuit 30 of the engine 10, as shown in FIG. 1.

The engine 10 is a water-cooled internal combustion engine, and includes the exhaust pipe 11, through which exhaust gas generated by a fuel combustion in the engine 10 flows. The exhaust pipe 11 includes a catalytic converter 12 for cleaning exhaust gas. Further, the engine 10 includes a radiator circuit 20, the exhaust gas recovery circuit 30 and a heater circuit 40. Coolant for cooling the engine 10 circulates in each of the radiator circuit 20 and the exhaust gas recovery circuit 30. The heater circuit 40 heats air-conditioning air by using the coolant (warm-water).

The radiator circuit 20 includes a radiator 21, a water pump 22 for making coolant to circulate, a passage 23 for bypassing the radiator 21 and a thermostat 24. The radiator 21 cools coolant by exchanging heat with outside air. The thermostat 24 controls an amount of coolant flowing through the radiator 21 and an amount of coolant flowing through the passage 23. Especially, when warm-up of the engine 10 is performed, the amount of coolant flowing through the passage 23 is increased so as to promote the warm-up of the engine 10. That is, supercooling of coolant by the radiator 21 can be reduced.

The exhaust heat recovery circuit 30 is branched from the radiator circuit 20 at an outlet of the engine 10, and connected to the water pump 22. Due to the water pump 22, coolant can circulate. A water tank 140 (condenser 130) of the recovery apparatus 100 is connected to the recovery circuit 30. The water tank 140 (condenser 130) will be described below.

Coolant (warm-water) is discharged into the heater circuit 40 from the engine 10 at a position different from the outlet for the radiator circuit 20, and the heater circuit 40 joins to a downstream side of the exhaust heat recovery circuit 30. A heater core 41 is arranged in the heater circuit 40, and operates as a heat exchanger for heating. The coolant (warm-water) circulates in the heater circuit 40 due to the water pump 22. The heater core 41 is arranged in an air-conditioning case of an air-conditioning unit (not shown). Air-conditioning air is sent by a fan (not shown), and the heater core 41 heats the air-conditioning air by exchanging heat with the warm-water.

As shown in FIG. 2, the recovery apparatus 100 includes a loop-type heat pipe 101, in which an evaporator 110 and the condenser 130 are connected to each other by a connection passage 115 and a reflux passage 135. The evaporator 110 is disposed in a duct 120, and the condenser 130 is disposed in the water tank 140.

The heat pipe 101 has a filling part (not shown), and is evacuated (depressurized) through the filling part. Then, working fluid (water) is filled in the heat pipe 101 through the filling part. Thereafter, the filling part of the heat pipe 101 is sealed. Water has a boiling point of 100° C. at one atmosphere. However, water in the heat pipe 101 has the boiling point of 5-10° C., because the heat pipe 101 is depressurized to 0.01 atmosphere, for example. In addition, alcohol, fluorocarbon or chlorofluorocarbon may be used as the working fluid other than water.

Parts (to be described below) of the recovery apparatus 100 are made of a stainless material having a high performance for enduring corrosion. The parts are integrally brazed using a brazing material at a joint or fitting part, after the parts are assembled.

The evaporator 110 includes tubes 111, fins 112, a bottom tank 113 and a top tank 114. The tube 111 is a long and thin pipe having a flat shape, and a longitudinal direction of the tube 111 corresponds to an up-and-down direction in FIG. 2. The tubes 111 are arranged in a width direction corresponding to a left-and-right direction in FIG. 2, and a predetermined tube pitch (interval) is provided between the tubes 111. Further, the tubes 111 are arranged in a thickness direction perpendicular to the tube longitudinal direction and the width direction.

The fin 112 made of a thin wall material is disposed between the tubes 111 in the width direction, and is connected to each outer wall (face) of the tubes 111. The fin 112 will be described below.

The bottom tank 113 is a flat container, and disposed at a bottom end of the tube 111 in the longitudinal direction. The top tank 114 is a flat container, and disposed at a top end of the tube 111 in the longitudinal direction. Each of the bottom tank 113 and the top tank 114 has a hole (not shown), and the tube 111 is inserted into the hole to be connected to the tank 113, 114. Thus, the tube 111 can communicate with the tank 113, 114.

The evaporator 110 is disposed in the duct 120. The duct 120 is a cylinder having a cross-section of rectangle, and exhaust gas flows inside of the duct 120 as described below. The evaporator 110 is disposed in the duct 120 such that the thickness direction corresponds to a flowing direction of the exhaust gas.

The condenser 130 includes a tube 131, a fin 132, a bottom tank 133 and a top tank 134. A longitudinal direction of the tube 131 corresponds to the up-and-down direction in FIG. 2. The fin 132 is formed into a crank shape, and disposed between the tubes 131 so as to be connected to the tubes 131. The tube 131 is connected to the tank 133, 134 so as to communicate with the tank 133, 134.

The condenser 130 is disposed in the water tank 140. The water tank 140 is a container elongated to correspond to the longitudinal direction of the tube 131. An introducing pipe 141 for introducing coolant into the water tank 140 is disposed at an end of the water tank 140, and a discharging pipe 142 for discharging coolant outward is disposed at the other end of the water tank 140.

The condenser 130 is disposed at a side of the evaporator 110. The top tank 114 of the evaporator 110 and the top tank 134 of the condenser 130 are connected by the connection passage 115 passing through the duct 120 and the water tank 140. Further, the bottom tank 113 of the evaporator 110 and the bottom tank 133 of the condenser 130 are connected by the reflux passage 135 passing through the duct 120 and the water tank 140. Therefore, the heat pipe 101 is formed by connecting the bottom tank 113, the tube 111, the top tank 114, the connection passage 115, the top tank 134, the tube 131, the bottom tank 133 and the reflux passage 135 in a loop in this order.

A clearance is provided between the duct 120 and the water tank 140. Positions of the connection passage 115 and the reflux passage 135 correspond to a position of the clearance, so that the passages 115, 135 operate as a thermal insulation part 121 between the evaporator 110 and the condenser 130.

A thin-wall band plate is formed into a wave shape by a roller process so as to make the fin 112 to be corrugated. As shown in FIG.3, the fin 112 is separated into plural fin layers in the width direction between the tubes 111. Here, in the first embodiment, the fin 112 is separated into two fin layers 1121, 1122. Each of the fin layers 1121, 1122 is connected to a wall (face) of the tube 111 by forming a fillet of brazing.

Further, a separation plate 116 made of a thin-wall board material is provided between the fin layers 1121, 1122. The plate 116 is connected to one of the fin layers, and is not connected to the other fin layer. In this embodiment, the plate 116 is connected to the fin layer 1122, and is not connected to the fin layer 1121 so as to form an operation force reducing part 112 a (non-connection part), which is displaceable relative to the plate 116 and the fin layer 1122. Alternatively, the plate 116 may be connected to the fin layer 1121, and is not connected to the fin layer 1122 so as to form the non-connection part 112 a

As described above, the evaporator 110 (duct 120) of the recovery apparatus 100 is disposed in the exhaust pipe 11 at downstream side of the catalytic converter 12, and the introducing pipe 141 and the discharging pipe 142 of the recovery apparatus 100 are connected to the exhaust heat recovery circuit 30.

Next, operation and advantage of the recovery apparatus 100 will be described. When the engine 10 is actuated, the water pump 22 is also actuated so that coolant circulates in the radiator circuit 20, the exhaust heat recovery circuit 30 and the heater circuit 40. Exhaust gas generated in the engine 10 flows in the exhaust pipe 11 through the catalytic converter 12, and is discharged outside through the evaporator 110 of the recovery apparatus 100. Further, coolant circulating in the exhaust heat recovery circuit 30 passes through the water tank 140 (condenser 130) of the recover apparatus 100.

After the engine 10 is actuated, water in the evaporator 110 of the heat pipe 101 receives heat from exhaust gas flowing in the duct 120 so as to be vaporized. The vapor rises through the tube 111, and flows into the condenser 130 (the top tank 134 and the tube 131) through the top tank 114 and the connection passage 115. Vapor flowing into the condenser 130 is cooled by coolant flowing from the exhaust heat recovery circuit 30 into the water tank 140, and condensed into condensed water. The condensed water returns to the bottom tank 113 of the evaporator 110 through the reflux passage 135.

Heat is transmitted from exhaust gas to water, that is, heat is transported from the evaporator 110 to the condenser 130. Then, the transmitted heat is emitted as condensed latent heat, when vapor is condensed in the condenser 130. Thus, coolant flowing through the exhaust heat recovery circuit 30 is heated in a positive manner. That is, the engine 10 can be more effectively warmed up. Therefore, friction loss of the engine 10 can be reduced, and fuel for improving cold startability can be reduced. Thus, gas mileage (fuel-efficiency) can be improved. Further, warming performance of the heater circuit 40 (heater core 41) using coolant as a heat source can be improved. In addition, a part of heat of exhaust gas is conducted (transmitted) from the evaporator 110 to the condenser 130 through the outer wall of the heat pipe 101.

Further, because the plural tubes 111 and the plural fins 112 are provided in the evaporator 110, area for receiving heat from exhaust gas can be increased. Therefore, evaporation of the working fluid can be accelerated in the evaporator 110, and heat transportation amount from the evaporator 110 to the condenser 130 can be increased.

Further, because the thermal insulation part 121 is provided between the evaporator 110 and the condenser 130, the evaporator 110 is restricted from being cooled by coolant in the condenser 130. Thus, condensing operation in the evaporator 110 can be reduced.

In the first embodiment, the fin 112 of the evaporator 110 is separated into the fin layers 1121, 1122, and the non-connection part 112 a (operation force reducing part) is provided between the fin layers 1121, 1122. The fin layers 1121, 1122 are not connected to each other, due to the non-connection part 112 a. For example, if a flow of exhaust gas has temperature distribution in the duct 120, temperature difference is generated between the tubes 111, so that a thermal expansion difference is generated between the tubes 111. However, in this embodiment, due to the non-connection part 112 a, tensile force (operation force) applied to the fin layer 1121, 1122 can be reduced. That is, the fin layers 1121, 1122 are displaceable between the tubes 111 in accordance with the thermal expansion of the tubes 111. Therefore, the fin layers 1121, 1122 are restricted from being damaged, because the operation force applied to the fin layers 1121, 1122 can be reduced.

Further, because the plate 116 is arranged between the fin layers 1121, 1122, a peak (valley) of the fin layer 1121 and a peak (valley) of the fin layer 1122 do not overlap (contact) with each other, when the fin layers 1121, 1122 are assembled between the tubes 111. Thus, the fin layers 1121, 1122 can be easily assembled.

The fin 112 is separated into the two fin layers 1121, 1122. However, the fin 112 may be separated into three layers 1121, 1122, 1123, as shown in FIG. 4. In this case, the plate 116 is arranged between opposing fin layers 1121, 1122, (1122, 1123). Further, the fin 112 may be separated into four or more fin layers, and the plate 116 may be arranged between opposing fin layers.

Second Embodiment

A second embodiment will be described with reference to FIGS. 5 and 6. Only one corrugated fin 112 is disposed between the tubes 111 in the width direction in the second embodiment. The fin 112 has a bent part 112 b (operation force reducing part) at the midpoint of the fin 112 between the tubes 111. The other parts in the second embodiment will be made similar to the first embodiment.

As shown in FIG. 5, the bent part 112 b is formed by bending the fin 112 at an approximately center position between the tubes 111, and has an obtuse angle. However, the bent part 112 b may have an acute angle. Alternatively, as shown in FIG. 6, the bent part 112 b is formed by bending the whole fin 112 between the tubes 111 like a S-letter shape.

Thereby, when the thermal expansion difference is generated between the tubes 111 in the tube longitudinal direction, operation force is not directly applied to the fin 112 until when the bent part 112 b becomes a linear shape. Thus, the fin 112 can be restricted from being damaged.

The bent part 112 b may be formed into other shape such as a wave other than the shapes shown in FIGS. 5 and 6. Further, the fin 112 may be a plate fin other than the corrugated fin.

Third Embodiment

A third embodiment will be described with reference to FIG. 7. The reflux passage 135 connecting the condenser 130 and the evaporator 110 includes a valve mechanism 150 in the third embodiment. The other parts in the third embodiment will be made similar to the first and second embodiments.

The valve mechanism 150 is made of a diaphragm, and opens and closes the reflux passage 135 in accordance with an inner pressure of the heat pipe 101, for example. The inner pressure of the heat pipe 101 corresponds to a pressure of the working fluid. When the inner pressure of the heat pipe 101 is larger than a predetermined value, the valve mechanism 150 closes the reflux passage 135. When the inner pressure of the heat pipe 101 is equal to or smaller than the predetermined value, the valve mechanism 150 opens the reflux passage 135.

After the engine 10 is actuated, coolant temperature is increased, and the inner pressure of the heat pipe 101 is gradually increased. In addition, the inner pressure of the heat pipe 101 is varied in accordance with an operation state, e.g., acceleration, deceleration, or stop, of the vehicle, because an amount of exhaust heat is varied by a load for the engine 10.

When the inner pressure of the heat pipe 101 is equal to or smaller than the predetermined value, the valve mechanism 150 opens the reflux passage 135. Then, heat is transported from exhaust gas to coolant. That is, exhaust gas recovery is performed.

Thereafter, when the coolant temperature becomes larger than a predetermined value (70° C.), and when the inner pressure of the heat pipe 101 is larger than the predetermined value, the valve mechanism 150 closes the reflux passage 135. Thus, reflux of condensed water in the heat pipe 101 is stopped. Then, water in the evaporator 110 is completely evaporated (the evaporator 110 is dried out), and the vapor flows into the condenser 130. Further, the vapor is condensed into water, and the condensed water is stored in the condenser 130.

That is, thermal transportation (exhaust heat recovery) due to the vaporizing and the condensing is stopped. Thus, only the thermal conduction (transmission) through the outer wall of the heat pipe 101 is performed so as to transmit heat to the coolant side. If the exhaust heat recovery is continued while exhaust gas temperature is increased due to an increased load of the engine 10, the coolant temperature may be too much increased. In this case, the radiator 21 may be overheated, because a load applied to the radiator 21 exceeds its capacity. However, in this embodiment, the radiator 21 can be prevented from being overheated, because the exhaust heat recovery can be stopped.

If the inner pressure of the heat pipe 101 becomes equal to or smaller than the predetermined value, the valve mechanism 150 opens the reflux passage 135 again, and the thermal transportation (exhaust heat recovery) can be restarted.

Here, when the exhaust heat recovery is restarted, the valve mechanism 150 opens the reflux passage 135 so that working fluid is returned to the tube 111 of the evaporator 110 from the condenser 130. At this time, flowing amount of the working fluid becomes different among the tubes 111, due to a difference in a distance between the valve mechanism 150 and each tube 111. Therefore, the thermal expansion difference is easily generated by the difference in the flowing amount of the working fluid, in addition to the temperature distribution in the flow of exhaust gas. Then, the thermal expansion difference generates operation force, and the operation force may damage the fin 112. However, in this embodiment, due to the operation force reducing part (the non-connection part 112 a and the bent part 112 b) of the fin 112, the fin 112 can be restricted from being damaged. Thus, when the recovery apparatus 100 includes the valve mechanism 150, the operation force reducing part 112 a, 112 b can be effective.

The valve mechanism 150 is the diaphragm for opening and closing the reflux passage 135 in accordance with the pressure of working fluid. However, the valve mechanism 150 may be a thermostatic valve using wax for opening and closing the reflux passage 135 in accordance with a temperature of coolant or working fluid.

Other Embodiments

In the above embodiments, the condenser 130 is arranged at the side of the evaporator 110. However, the condenser 130 may be arranged above the evaporator 110. In this case, the tube 131 of the condenser 130 is horizontally arranged.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. An exhaust heat recovery apparatus comprising: an evaporator having a plurality of tubes arranged in an arrangement direction, and a fin for increasing an area for transmitting heat, the evaporator evaporating working fluid therein by heat of exhaust gas discharged from an internal combustion engine; and a condenser for emitting heat of the working fluid flowing from the evaporator toward coolant of the internal combustion engine so as to condense the working fluid, and returning the condensed working fluid to the evaporator, wherein the fin is disposed between the tubes in the arrangement direction, and connected to a face of the tube, the fin has an operation force reducing part for reducing an operation force applied to the fin in accordance with a thermal expansion difference between the tubes in a tube longitudinal direction, and the operation force reducing part is disposed at a midpoint of the fin in the arrangement direction.
 2. The exhaust heat recovery apparatus according to claim 1, wherein the fin is a corrugated fin having a wave shape, and separated into a plurality of fin layers in the arrangement direction, and the operation force reducing part is a non-connection part such that opposing fin layers are not connected to each other.
 3. The exhaust heat recovery apparatus according to claim 2, further comprising a separation plate for separating the opposing fin layers, wherein the separation plate is connected to only one of the opposing fin layers.
 4. The exhaust heat recovery apparatus according to claim 1, wherein the fin is a corrugated fin having a wave shape, and separated into a plurality of fin layers in the arrangement direction, and opposing fin layers are displaceable between the tubes, when at least one of the opposing fin layers has the operation force reducing part.
 5. The exhaust heat recovery apparatus according to claim 4, further comprising a separation plate for separating the opposing fin layers, wherein the separation plate is connected to only one of the opposing fin layers.
 6. The exhaust heat recovery apparatus according to claim 1, wherein the operation force reducing part is a bent part, at which the midpoint of the fin is bent.
 7. The exhaust heat recovery apparatus according to claim 6, wherein the bent part is disposed at an approximately center position of the fin between the tubes in the arrangement direction, and the bent part has an obtuse angle.
 8. The exhaust heat recovery apparatus according to claim 6, wherein the bent part has a S-letter shape.
 9. The exhaust heat recovery apparatus according to claim 6, wherein the fin is a corrugated fin having a wave shape.
 10. The exhaust heat recovery apparatus according to claim 1, further comprising a valve mechanism for opening and closing a passage, through which the working fluid returns from the condenser to the evaporator, in accordance with at least one of a pressure of the working fluid, a temperature of the coolant and a temperature of the working fluid. 